Chapter 5 Reservoir Operations

Chapter 5 - Reservoir Operations Reservoir’s Authorized Purposes Box Butte Dam impounds water from the Niobrara River to form Box Butte Reservoir. The authorized purposes of Box Butte Dam and Reservoir are to provide storage for irrigation, recreation, fish and wildlife, and sediment control. Contract between the Mirage Flats Irrigation District, the Nebraska Game and Parks Commission and the United States In March, 1990 the District, the Commission, and Reclamation entered into an agreement to establish a minimum pool elevation at Box Butte Reservoir of 3978.0 ft. to support and maintain a viable fishery resource in Box Butte Reservoir. This agreement was modified in March, 2000 to add one foot to the minimum pool elevation (3979.0 ft). (See Appendix A5) This agreement is in effect through 2025. These reservoir elevations raised the lowest allowable operating elevation from the previous historical level of 3976.5 ft. At higher reservoir elevations, an effort should be made to provide as near optimum conditions as possible for fisheries and recreation while meeting the other authorized purposes. It is clearly understood that the primary purpose of Box Butte Reservoir is the delivery of water from the storage space for irrigation purposes and that the reservoir level will fluctuate widely above the 3979.0 ft. minimum elevation. There is no agreement for a minimum reservoir releases to the Niobrara River for fish and wildlife purposes. Reservoir Operations and Flood Control

The Nebraska-Kansas Area Manager in Grand Island, Nebraska, is responsible for the O&M of the dam and reservoir and appurtenant features. Box Butte Reservoir is not a flood control storage reservoir. Reservoir capacity allocations (storage capacity in relation to water elevations) are shown in Table 6, followed by definitions of the various types of storage. Table 7 shows historic maximum/minimum reservoir levels for 1965 to 2007. No reservoir elevation data is available prior to 1965.

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Table 6 – Box Butte Reservoir Capacity Allocations

Space Net Capacity (acre-ft) Water Elevation (feet msl)

Dead Storage1 188 3,969.0Inactive Storage2 2,204 3,979.0Conservation Storage3 27,769 4,007.0No Flood Pool ----- ----- Surcharge Pool4 16,740 4,016.0

1 Dead Storage: Capacity from which stored water cannot be evacuated by gravity. 2 Inactive Storage: Capacity that can be released from the dam but is below design capacity for irrigation. 3Conservation Storage: The pool allocated to storage of water for irrigation purposes only.

4Surcharge Pool: Capacity between the top of conservation pool (4007.0) and the maximum water surface elevation (4016.0)

Reservoir Operations and Fisheries

The reservoir experiences extreme water draw-downs usually within a two month period during the summer. This results not only in an extreme loss of benthic fauna and shoreline habitat, but also significant losses in young-of-year fish. Drawdowns concentrate the predators, prey, and fishermen in one small area. The results are that prey is consumed, the predators get larger, and the fishermen catch more fish. This can be a healthy situation if the prey base does not collapse or the angler pressure does not become too extensive.

TOP OF INACTIVE=3979.00

TOP OF CONS.=4007.004,01

4,00

4,00

3,99

3,99

3,98

3,98

3,97

3,97

3,96

10 YEAR RESERVOIR LEVELS

ELEV

ATI

ON

(F

T.)

9 9 2 0 0 0 0 0 0 0

JAN 1998 - DEC 2007

Figure 10 – Box Butte Reservoir 10-Year Reservoir Level

BOX

Reservoir Operations and Recreation

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Reservoir Operations

Recreational use of reservoir facilities is somewhat restricted during low-water levels and causes some public-use inconvenience. The fluctuating water levels expose once submerged objects which may become safety hazards to boaters. The Commission does not place buoys around the exposed objects. The bottom of the concrete at the low water boat ramp is elevation 3979.6. Table 7 – Maximum and Minimum Reservoir Levels

Year

Date Max Level (feet msl)

Contents (acre-feet)

Date Min. Level (feet msl)

Contents (acre-feet)

1965 May 20 4002.55 24,440 Sept. 7 3979.62 3,530 1966 July 11 4002.10 23,790 Oct. 11 3983.00 5,300 1967 July 11 4002.08 23,793 Sept. 10 3986.59 7,560 1968 June 23 4003.34 25,555 Sept. 15 3990.21 10,455 1969 May 26 4001.90 23,546 Sept. 12 3978.30 2,950 1970 June 15 3999.35 20,181 Sept. 6 3971.68 1,105 1971 June 27 3999.72 20,652 Sept. 4 3970.42 868 1972 June 30 3996.49 16,749 Sept. 9 3976.24 2,211 1973 June 12 3999.32 20,143 Sept. 6 3972.95 1,368 1974 May 15 3998.51 19,132 Aug. 30 3975.22 1,918 1975 May 31 3996.51 16,761 Aug. 30 3970.44 872 1976 June 30 3994.31 14,391 Aug. 23 3969.82 764 1977 June 19 3994.90 15,009 Aug. 31 3980.18 3,808 1978 June 10 3997.75 18,214 Sept. 11 3975.75 2,067 1979 May 31 3995.81 15,993 Sept. 15 3980.50 3,962 1980 May 31 3998.84 19,540 Sept. 5 3979.58 3,515 1981 June 10 3995.83 16,015 Sept. 10 3975.70 2,052 1982 July 9 3996.09 16,301 Sept. 14 3981.48 4,470 1983 June 30 4001.11 22,475 Sept. 10 3985.73 6,968 1984 June 30 4000.30 21,402 Sept. 7 3978.15 2,889 1985 May 31 3995.28 15,416 Aug. 26 3969.00 640 1986 June 30 3997.70 18,155 Sept. 8 3976.80 2,391 1987 May 20 3998.40 18,996 Sept. 1 3974.80 1,806 1988 June 21 3996.10 16,312 Aug. 30 3973.01 1,381 1989 May 30 3992.09 12,186 Aug. 16 3969.00 640 1990 June 14 3992.47 12,550 Aug. 17 3980.47 3,947 1991 July 1 3998.47 19,082 Aug. 31 3984.08 5,925 1992 July 8 3997.57 18,000 Sept. 6 3894.97 6,473 1993 July 7 3999.75 20,691 Sept. 13 3985.76 6,988 1994 May 27 3999.96 20,961 Aug. 31 3983.15 5,384 1995 July 4 4000.56 21,743 Sept. 15 3984.60 6,242 1996 June 16 3999.46 20,320 Aug. 28 3987.40 8,150 1997 June 24 4000.03 21,051 Sept. 5 3988.49 8,997 1998 May 22 4000.10 21,142 Sept. 4 3988.89 9,324 1999 July 5 4001.43 22,907 Sept. 3 3988.95 9,374 2000 June 1 4002.14 23,876 Sept. 2 3988.67 9,143 2001 July 14 4000.36 21,481 Sept. 7 3986.34 7,384 2002 May 31 3997.55 17,976 Aug. 21 3979.87 3,652 2003 July 8 3994.12 14,195 Aug. 24 3979.72 3,579 2004 May 19 3991.78 11,893 Aug. 31 3979.39 3,423 2005 June 28 3995.04 15,158 Sept. 3 3982.95 5,270 2006 May 17 3994.98 15,094 Sept. 11 3979.92 3,676 2007 June 21 3991.30 11,444 Aug. 13 3978.91 3,204 (No reservoir elevation data available prior to 1965) (Note: new area capacity tables effective January 1, 2008) The Mirage Flats Project map is on page 52a; please refer to it for more

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information. Downstream Releases and Operations Land The dam, outlet works, and delivery system is operated and maintained by the MFID for the protection of project facilities. The majority of Federal lands located on the downstream side of Box Butte Dam is designated as a WMA, operated and maintained by the Commission. Reclamation retains primary jurisdiction over the designated operations area. Reclamation retains full access to and unlimited use of any area developed for wildlife habitat, if required for the purpose of ensuring proper operations and protection of Box Butte Dam/Reservoir. The District’s contracted irrigation season is from April through September. Irrigation water can be released any time during this period, although the District typically takes water from late June through August. The District has a storage right to store water in Box Butte Reservoir, a supplemental irrigation water right for the release of District water, and a natural flow right for surface water from the Niobrara River. The storage rights, supplemental irrigation right, and appropriated natural flow rights are used in combination with each other to meet the water supply needs for 11,662 acres of irrigable project lands in the District. Water is released from Box Butte Reservoir to the Niobrara River and diverted into the Mirage Flats Canal at the Dunlap Diversion Dam. The diversion dam is located approximately 8 miles downstream of the reservoir. See Mirage Flats Project map on page 52a. Ground-water depletions of the base flow and numerous farm conservation practices have greatly reduced inflow to the reservoir. Since the mid 1950s the surface water supply in the Niobrara River basin has decreased significantly (see Figures 2 & 11). The average annual precipitation amount has been generally steady while the average annual reservoir inflow continues to decline. The 10-year average annual inflow to Box Butte Reservoir has decreased from 22,100 acre-feet from 1947 through 1956, to 19,400 acre-feet from 1977 through 1986, to 16,200 acre-feet from 1997 through 2006. Although the District has access to the entire conservation pool of 27,816 acre-feet of water, plus the inflow, average annual release from Box Butte Reservoir for irrigation over the past 10 years has been approximately 11,800 acre-feet. This average is reduced to approximately 9,800 acre-feet over the past 5 years. This decrease in reservoir inflow has drastically changed District operations. The reduced inflow has created lower pool levels, and the increased demands cause a greater fluctuation in water levels. See Table 7 for historic maximum/minimum reservoir levels for Box Butte Reservoir. Reclamation and the District are very concerned with the historic increase of groundwater development above Box Butte Reservoir and the close correlation with the decrease in reservoir inflows. Reclamation will continue to work with the Upper Niobrara White Natural

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Reservoir Operations

53

Resources District and the Nebraska Department of Natural Resources in the development of the Integrated Water Management Plan. This plan provides a mechanism to reduce the groundwater level declines for those areas where the groundwater is hydrologically connected to the streams. With the plan in place reservoir inflows may return to the pre-development condition.

BOX BUTTE RESERVOIRInflow & Outflow

0

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76 78 80 82 84 86 88 90 92 94 96 98 00 02 04 06

Y E A R

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00 A

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ET

Figure 11 – Box Butte Reservoir Inflow/Outflow